Regulating devices that are intended for control of liquid flow and/or pressure, are known in various embodiments.
In certain applications there exists a need to control the flow and/or pressure so that the flow and/or pressure may be accurately set to a desired value. One such application is the field of dynamometer testing of motor vehicles.
Here a testing device is adapted to be drivingly connected to a driven vehicle output shaft and comprises means for measuring one or more quantities significant to the performance of the engine and the transmission, such as the torque that the driven shaft applies to a power-absorbing device forming part of the device.
EP 0 210 979 discloses an device comprising load absorbing means in the form of a hydrostatic pump assembly which has an input shaft adapted to be in engagement with a driven vehicle shaft using a rigid coupling. The pump assembly consists of two pumps that are drivingly interconnected and thus are both driven by the shaft. An adjustable control valve is controlled such that the valve allows the passage of a liquid flow, the volumetric rate of which being related to the desired rotational speed of the rotor, i.e. of the driven vehicle shaft.
A problem with known regulating devices, however, is that they do not provide an accurate control fast enough for certain applications. For example, the known dynamometer testing device can not be used for precise testing of an engine during rapidly changing dynamic processes, such as rapid accelerations, since the response from the control valve cannot be controlled sufficiently fast.
In WO 01/86113 a sleeve valve is described, wherein a sleeve is arranged movably inside a housing. The sleeve and the housing are provided with corresponding apertures for adjustment of the flow by bringing the apertures in and out of correspondence with each other by rotation of the sleeve relative to the housing. This known device is, however., not suitable for dynamic regulation of liquid flows.